1. Field of the Invention
The present invention relates to a printing apparatus and an ink amount detection method. In particular, the invention relates to the ink amount detection for a main tank in an ink supply system including a sub tank for directly supplying ink to a print head and the main tank for containing ink to be supplied to the sub tank.
2. Description of the Related Art
An ink supply system of an inkjet printing apparatus which includes a main tank and a sub tank allows the printing apparatus to continue a printing operation using ink in the sub tank even when there is no more ink in the main tank for example. One configuration to fill the sub tank with ink from the main tank in the ink supply system as described above is disclosed in Japanese Patent Laid-Open No. 2012-096363. According to Japanese Patent Laid-Open No. 2012-096363, when a liquid level detection unit in the sub tank detects that the amount of ink in the sub tank is reduced to a level lower than a predetermined liquid level, then an ink filling mechanism fills the sub tank with a predetermined amount of ink from the main tank. Then, when the ink filling operation is completed and when the liquid level detection unit detects that the ink liquid level in the sub tank is again equal to or higher than the predetermined liquid level, it is determined that the sub tank is filled with ink and a subsequent printing operation for example is performed.
In the ink supply system in such a configuration, even when an operation to fill a predetermined amount of ink is repeated a predetermined times while the liquid level detection unit in the sub tank detects the liquid level is lower than the predetermined liquid level, a case may be caused in which it may be determined that there is ink shortage in the main tank if the liquid level in the sub tank is lower than the predetermined liquid level.
However, in such a configuration, regardless of the amount of ink remaining in the main tank, the predetermined number of ink filling operations may be repeated and ink shortage in the main tank may be determined if the liquid level in the sub tank does not reach a predetermined liquid level or more. Thus, if the amount of ink in the main tank is small for example, the amount of ink that can be filled by a single filling operation may be lower than the above described predetermined amount. In this case, even when the predetermined number of the filling operations as a reference is repeated, the predetermined liquid level is not reached, thus consequently causing the predetermined number of the filling operations to be unnecessary. This means that unnecessary ink filling operations are performed to cause a proportional increase of time required to determine there is ink shortage in the main tank.